Sorption, desorption and mineralisation of the herbicides glyphosate and MCPA in samples from two Danish soil and subsurface profiles

Sustained anaerobic degradation of 4-chloro-2-methylphenoxyacetic acid by acclimated sludge in a continuous-flow reactor

4-Chloro-2-methylphenoxyacetic acid (MCPA) is a widely used herbicide across the world. MCPA is persistent and easily transports into anoxic environment, such as groundwater, sediments and deep soils. However, little research on anaerobic microbial degradation of MCPA was carried out. The functional microorganisms as well as the catabolic pathway are still unknown. In this research, an anaerobic MCPA-degrading bacterial consortium was enriched from the river sediment near a pesticide-manufacturing plant. After about 6 months' acclimation, the MCPA transformation rate of the consortium reached 4.32 μmol g^-1 day^-1, 25 times faster than that of the original sludge. 96% of added MCPA (2.5 mM) was degraded within 9 d of incubation. Three metabolites including 4-chloro-2-methylphenol (MCP), 2-methylphenol (2-MP) and phenol were identified during the anaerobic degradation of MCPA. An anaerobic catabolic pathway was firstly proposed: firstly, MCPA was transformed to MCP via the cleavage of the aryl ether, then MCP was reductively dechlorinated to 2-MP which was further demethylated to phenol. The 16S rRNA gene amplicon sequencing revealed a substantial shift in the bacterial community composition after the acclimation. SBR1031, Acidaminococcaceae, Aminicenantales, Syntrophorhabdus, Acidaminobacter, Bacteroidetes_vadinHA17, Methanosaeta, Bathyarchaeia, KD4-96, Anaeromyxobacter, and Dehalobacter were significantly increased in the enriched consortium after acclimation, and positively correlated with the anaerobic degradation of MCPA as suggested by heat map correlation analysis. This study provides a basis for further elucidation of the anaerobic catabolism of MCPA, and contributes to developing efficient and low-cost anaerobic treatment technologies for MCPA pollution.

Detoxification and metabolism of glyphosate by a Pseudomonas sp. via biogenic manganese oxidation

Biogenic manganese oxides (BMO) are widely distributed in groundwater and provides promise for adsorbing and oxidizing a wide range of micropollutants, however, the continuous biodegradation and bioavailability of micropollutants via cycle biogenic Mn(II) oxidation remains to be elucidated. In this study, glyphosate was degraded and to serve as the nutrient source by a Pseudomonas sp. QJX-1. The addition of glyphosate will not affect the Mn(II) oxidation function of the strain but will affect its Mn(II) oxidation process and effect. The glyphosate degradation products could further be used as the C, N and P sources for bacterium growth. Analysis of the RNA-seq data suggested that Mn(II) oxidation driven by oxidoreductases for glyphosate degradation. The long-term column experiments using biological Mn(II) cycling to realize continuous detoxification and metabolism of glyphosate, and thus revealed the synergism effects of biological and chemical conversion on toxic micropollutants and continuous metabolism in an aquatic ecosystem.

Heavy rainfall following a summer drought stimulates soil redox dynamics and facilitates rapid and deep translocation of glyphosate in floodplain soils

We present field data on the effects of heavy rainfall after drought on the mobility of glyphosate and redox conditions in a clayey floodplain soil. By applying glyphosate together with deuterated water as conservative tracer in combination with time resolved in situ redox potential measurements, the spatial and temporal patterns of water infiltration and pesticide transport as well as the concomitant changes of the redox conditions were revealed. Our findings demonstrate that shrinkage cracks in dry soils can serve as effective transport paths for atmospheric oxygen, water and glyphosate. The rain intensity of a typical summer storm event (approx. 25 mm within one hour) was sufficient to translocate deuterated water and glyphosate to the subsoil (50 cm) within 2 hours. Soil wetting induced partial closure of the shrinkage cracks and stimulated microbial activity resulting in pronounced dynamics of in situ soil redox conditions. Redox potentials in 40 to 50 cm depth dropped permanently to strongly reducing conditions within hours to days but fluctuated between reducing and oxidizing conditions in 10 to 30 cm depth. Our findings highlight the close link between the presence of macropores (shrinkage cracks), heavy rainfall after drought, redox dynamics and pesticide translocation to the subsoil and thus call for further studies addressing the effects of dynamic redox conditions as a limiting factor for glyphosate degradation.

Environmental fate of glyphosate used on Swedish railways - Results from environmental monitoring conducted between 2007-2010 and 2015-2019

Glyphosate herbicides are widely relied upon by European railway operators for controlling vegetation growing on railway tracks. In Sweden, concentrations of glyphosate and its main degradation product AMPA have been monitored in the groundwater close to railways during two monitoring periods: between 2007-2010 and 2015-2019. In total, 603 groundwater samples from 12 different monitoring sites and 645 soil samples from 5 of these sites were analyzed. Glyphosate and AMPA were detected in 16% and 14%, respectively, of groundwater samples taken from directly beneath the track, with concentrations exceeding the EU groundwater quality standard of 0.1 μg/L in 6 and 4% of the cases, respectively. The highest concentrations detected in single samples were 7 μg glyphosate/L and 1.1 μg AMPA/L. However, further horizontal spread in the groundwater zone appeared to be limited as glyphosate and AMPA were only detected in 1-3% of the groundwater samples taken from outside the track area itself, and since no difference was seen between water from reference and down-gradient wells. In the autumn of 2018, higher concentrations were detected in the groundwater from beneath 3 out of the 5 then active monitoring sites and a possible explanation is that the unusually hot and dry summer of 2018 limited degradation, thus leading to an increased susceptibility of leaching. The contents of glyphosate and AMPA in soil samples from three of the sites were very low (average < 0.05 mg/kg in soil from 0 to 30 cm), indicating that they were only sprayed to a limited degree, whereas the contents from two of the test sites were in line with what would be expected based on the used dose and a predicted half-life of about 4 ± 2 months (average 0.22-0.84 mg/kg). No signs of accumulation of glyphosate in the railway ballast over time were observed.

Behavior and fate of fungicide chlorothalonil in urban landscape soils and associated environmental concern

This novel study investigated the behavior and fate of chlorothalonil in terms of kinetics, sorption‒desorption and leaching potential in urban landscape soils using batch experiments. The pseudo-second-order model well described the sorption kinetics of chlorothalonil in urban soils. Consequently, chlorothalonil was partitioned into heterogeneous surfaces of soil following the Freundlich isotherm model. According to PCA, soil organic matter (OM), silt, clay, and oxides of Al and Fe exhibited a significant positive correlation (P < 0.05) with chlorothalonil K_d (P < 0.05), while sand content and soil pH showed a negative correlation at P < 0.05. In soils, decreased sorption of chlorothalonil was also due to the presence of undecomposed or partly decomposed OM, whereas increased sorption could be attributed to the combined effect of OM with C = O and C-H groups, silt, clay, Al and Fe oxides and hydrophobicity of the fungicide. Also, HI, GUS, LIX and K_d of four among nine urban soils indicated that chlorothalonil has a great potential for leaching into the groundwater from the soil surface, posing an unintended threat to non-target biota and food safety. Therefore, utmost care must be taken while applying chlorothalonil in urban landscapes, particularly on impervious surfaces, to minimize the impact on the ecosystem.

Superabsorbent polymer as a supplement substrate of constructed wetland to retain pesticides from agricultural runoff

Surface water runoff can export pesticides from agricultural fields into adjacent aquatic ecosystems, where they may pose adverse effects to organisms. Constructed wetlands (CWs) are widely used to treat agricultural runoff contaminated by pesticides, but the removal of hydrophilic pesticides is usually low. In this study, we suggest superabsorbent polymer (SAP), a cross-linked hydrophilic polymer, as a supplement to substrates of CWs and tested the hypothesis that SAP results in an enhanced removal of hydrophilic pesticides. Therefore, batch experiments were conducted to study the retention capacity of water-saturated SAP (w-SAP) for several hydrophilic pesticides. Retention of the pesticides on w-SAP was related to the ionization state and water solubility of the pesticides. The retention of neutral pesticides, imidacloprid, metalaxyl and propiconazole, was about 20% higher than that measured for anionic pesticides, bentazone, glyphosate and MCPA. The retention of the pesticides by w-SAP mainly resulted from their distribution in the gel-water phase of w-SAP, while less water soluble pesticides might have also been adsorbed on the molecular backbone of SAP. Furthermore, we tested the efficacy of w-SAP for treatment of runoff water contaminated by pesticides in lab-scale horizontal subsurface flow CWs. SAP in CWs improved the removal of the pesticides, including the recalcitrant ones. The removal enhancement was owing to the increase of hydraulic retention time and improvement of biodegradation. The removal of the pesticides in SAP containing CWs was > 93% for MCPA, glyphosate, and propiconazole, 62 - 99% for imidacloprid, 50 - 84% for metalaxyl, and 38 - 73% for bentazone. In the control gravel CWs, the removal was > 98% for glyphosate, generally > 83% for MCPA and propiconazole, 46 - 98% for imidacloprid, 32 - 97% for metalaxyl, and 9 - 96% for bentazone.

Retention and distribution of pesticides in planted filter microcosms designed for treatment of agricultural surface runoff

Pesticides in agricultural surface water runoff cause a major threat to freshwater systems. Installation of filter systems or constructed wetlands in areas of preferential run-off is a possible measure for pesticides abatement. To develop such systems, combinations of filter materials suitable for retention of both hydrophilic and hydrophobic organic pesticides were tested for pesticide removal in planted microcosms. The retention of six pesticides frequently detected in surface waters (bentazone, MCPA, metalaxyl, propiconazole, pencycuron, and imidacloprid) was evaluated in unplanted and planted pot experiments with novel bed material mixtures consisting of pumice, vermiculite, water super-absorbent polymer (SAP) for retention of ionic and water soluble pesticides, and synthetic hydrophobic wool for adsorption of hydrophobic pesticides. The novel materials were compared to soil with high organic matter content. The highest retention of the pesticides was observed in the soil, with a considerable translocation of pesticides into the plants, and low leaching potential, in particular for the hydrophobic compounds. However, due to the high retention of pesticides in soil, environmental risks related to their long term mobilization cannot be excluded. Mixtures of pumice and vermiculite with SAP resulted in high retention of i) water and ii) both hydrophilic and hydrophobic pesticides but with much lower leaching potential compared to the mineral systems without SAP. Mixtures of such materials may provide near natural treatment options in riparian strips and also for treatment of rainwater runoff without the need for water containment systems.

Plant litter enhances degradation of the herbicide MCPA and increases formation of biogenic non-extractable residues in soil

Amendment of soils with plant residues is common practice for improving soil quality. In addition to stimulated microbial activity, the supply of fresh soluble organic (C) from litter may accelerate the microbial degradation of chemicals in soils. Therefore, the aim of this study was to test whether the maize litter enhances degradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) and increases formation of non-toxic biogenic non-extractable residues (bioNERs). Soil was amended with ¹³C₆-MCPA and incubated with or without litter addition on the top. Three soil layers were sampled with increasing distance from the top: 0-2 mm, 2-5 mm and 5-20 mm; and the mass balance of ¹³C₆-MCPA transformation determined. Maize litter promoted microbial activity, mineralization of ¹³C₆-MCPA and bioNER formation in the upper two layers (0-2 and 2-5 mm). The mineralization of ¹³C₆-MCPA in soil with litter increased to 27% compared to only 6% in the control. Accordingly, maize addition reduced the amount of extractable residual MCPA in soil from 77% (control) to 35% of initially applied ¹³C₆-MCPA. While non-extractable residues (NERs) were <6% in control soil, litter addition raised NERs to 21%. Thereby, bioNERs comprised 14% of ¹³C₆-MCPA equivalents. We found characteristic differences of bioNER formation with distance to litter. While total NERs in soil at a distance of 2-5 mm were mostly identified as ¹³C-bioNERs (97%), only 45-46% of total NERs were assigned to bioNERs in the 0-2 and 5-20 mm layers. Phospholipid fatty acid analysis indicated that fungi and Gram-negative bacteria were mainly involved in MCPA degradation. Maize-C particularly stimulated fungal activity in the adjacent soil, which presumably facilitated non-biogenic NER formation. The plant litter accelerated formation of both non-toxic bioNERs and non-biogenic NERs. More studies on the structural composition of non-biogenic NERs with toxicity potential are needed for future recommendations on litter addition in agriculture.

The Effects of Glyphosate and Its Commercial Formulations to Marine Invertebrates: A Review

Glyphosate is the active ingredient of numerous commercial formulations of herbicides applied in different sectors, from agriculture to aquaculture. Due to its widespread use around the world, relatively high concentrations of glyphosate have been detected in soil and aquatic environments. The presence of glyphosate in aquatic ecosystems has aroused the attention of researchers because of its potential negative effects on living organisms, both animals and plants. In this context, this review intends to summarize results of studies aimed at evaluating the effects of glyphosate (both as active ingredient and component of commercial formulations) on marine invertebrates. Generally, data obtained in acute toxicity tests indicate that glyphosate and its commercial formulations are lethal at high concentrations (not environmentally realistic), whereas results of long-lasting experiments indicate that glyphosate can markedly affect biological responses of marine invertebrates. Consequently, more efforts should be addressed at evaluating chronic or sub-chronic effects of such substances to marine invertebrate species.

Decyl glucoside surfactant Triton CG-110 does not significantly affect the environmental fate of glyphosate in the soil at environmentally relevant concentrations

Glyphosate is the most common herbicide worldwide, and its impact on the environment has increasingly been scrutinized. Glyphosate-based formulations can contain co-formulants, among which are surfactants. This study aimed to investigate whether the presence of an alkyl polyglucoside-based surfactant, Triton CG-110, affects the adsorption, leaching, and mineralisation of glyphosate in the soil. The experiments were conducted in two soils with different textures (sandy and clay) and in washed sand. Glyphosate and surfactant mixtures were applied at realistic field rates. Because of ponding and scarce leaching from the field soil, the leaching experiments were conducted only with washed sand. The results indicate a reduction of glyphosate adsorption in washed sand (from K_f = 13.5 to 3.99 μg^1-1/n (ml)^1/n g^-1) and in sandy soil (from K_f = 165 to 90.8 μg^{1-1/ n} (ml)^1/n g^-1) when using a Triton CG-110 concentration of 0.5 %, which corresponds to that of a spraying solution applied in the field, whereas adsorption in clay soil was unaffected. Triton CG-110 did not significantly affect glyphosate leaching in washed sand or mineralisation in any of the tested soils. The results indicate that Triton CG-110 is unlikely to significantly affect the environmental fate of glyphosate in the soil at environmentally relevant concentrations.

Degradation of glyphosate in a Colombian soil is influenced by temperature, total organic carbon content and pH

Glyphosate is one of the most used herbicides in the world. The fate of glyphosate in tropical soils may be different from that in soils from temperate regions. In particular, the amounts and types of non-extractable residues (NER) may differ considerably, resulting in different relative contributions of xenoNER (sorbed and sequestered parent compound) and bioNER (biomass residues of degraders). In addition, environmental conditions and agricultural practices leading to total organic carbon (TOC) or pH variation can alter the degradation of glyphosate. The aim of this study is thus to investigate how the glyphosate degradation and turnover are influenced by varying temperature, pH and TOC of sandy loam soil from Colombia. The pH or TOC of a Colombian soil was modified to yield five treatments: control (pH 7.0, TOC 3%), 4% TOC, 5% TOC, pH 6.5, and pH 5.5. Each treatment received 50 mg kg-1 of 13C315N-glyphosate and was incubated at 10 °C, 20 °C and 30 °C for 40 days. Rising temperature increased the mineralization of 13C315N-glyphosate from 13 to 20% (10 °C) to 32-39% (20 °C) and 41-51% (30 °C) and decreased the amounts of extractable 13C315N-glyphosate after 40 days of incubation from 13 to 26% (10 °C) to 4.6-12% (20 °C) and 1.2-3.2% (30 °C). Extractable 13C315N-glyphosate increased with higher TOC and higher pH. Total 13C-NER were similar in all treatments and at all temperatures (47%-60%), indicating that none of the factors studied affected the amount of total 13C-NER. However, 13C-bioNER dominated within the 13C-NER pool in the control and the 4% TOC treatment (76-88% of total 13C-NER at 20 °C and 30 °C), whereas in soil with 5% TOC and pH 6.5 or 5.5 13C-bioNER were lower (47-61% at 20 °C and 30 °C). In contrast, the 15N-bioNER pool was small (between 14 and 39% of the 15N-NER). Thus, more than 60% of 15N-NER is potentially hazardous xenobiotic NER which need careful attention in the future.

Olive mill sludge may reduce water contamination by 4-chloro-2-methylphenoxyacetic acid (MCPA) in non-flooding but enhance it in flooding rice cropping agroecosystems

A field experiment covering three years was conducted to evaluate how composted olive mill sludge (OS) influenced MCPA's environmental fate in rice soils under six combinations of tillage and irrigation cultivation techniques: tillage and sprinkler irrigation without (TS) or with (TSOS) the addition of OS (80 Mg ha^-1), no-tillage and sprinkler irrigation without (NTS) or with (NTSOS) OS, and tillage and continuous flooding without (TF) or with (TFOS) OS. The measurements made in the first and third years after OS application were taken to constitute the "direct" and "residual" effects, respectively. After OS amendment, K_d (partition coefficients) values in the direct year were lower by factors of 1.1, 1.3, and 1.9 in TSOS, NTSOS, and TFOS, respectively, relative to the corresponding unamended soils, and in the residual year by factors of 1.1 and 1.5 in TSOS and NTOS, but greater by a factor of 1.5 in TFOS, than in the corresponding unamended soils, respectively. The dissipation of MCPA was very fast under both anaerobic (t_1/2 = 1.80-5.29 d) and aerobic (t_1/2 = 2.23-9.42 d) incubation conditions. The field application of OS led to a decrease in MCPA persistence under both incubation conditions, especially in the TF case. However, while under aerobic conditions the half-life (t_1/2) decreased after OS addition in the direct and residual years, under anaerobic condition it only decreased in the direct year. While the application of OS in TS and NTS led to less leaching of MCPA, in TF it led to 1.4 and 1.2 times more leaching losses of the herbicide for the direct and residual years, respectively. Therefore, the use of OS in rice production could be considered an effective strategy for reducing water contamination by MCPA in at least the short- and medium-terms after its application, but only under non-flooding crop management regimes irrespective of the tillage practice implemented.

Glyphosate: Its Environmental Persistence and Impact on Crop Health and Nutrition

Glyphosate-based herbicide products are the most widely used broad-spectrum herbicides in the world for postemergent weed control. There are ever-increasing concerns that glyphosate, if not used judiciously, may cause adverse nontarget impacts in agroecosystems. The purpose of this brief review is to present and discuss the state of knowledge with respect to its persistence in the environment, possible effects on crop health, and impacts on crop nutrition.

The pesticide mineralization capacity in sand filter units of drinking water treatment plants (DWTP): Consistency in time and relationship with intake water and sand filter characteristics

Sand filters (SFs) are commonly applied in drinking water treatment plants (DWTPs) for removal of iron and manganese but also show potential for microbial degradation of pesticide residues. The latter is advantageous in case the intake water contains pesticide residues. However, whether this involves mineralization suggesting no generation of harmful transformation products, its consistency over time, and how this ability relates to physicochemical and biological characteristics of the DWTP intake water and the SFs is unknown. The capacity to mineralize the herbicides bentazon and 2-methyl-4-chlorophenoxyacetic acid (MCPA) was examined in SF samples from 11 DWTPs differing in operation, intake water composition and pesticide contamination level. MCPA was mineralized in all biologically active SFs while mineralization of bentazon occurred rarely. Mineralization of both compounds was consistent in time and across samples taken from different SF units of the same DWTP. Kinetic modelling of mineralization curves suggested the occurrence of growth linked bentazon and MCPA mineralization in several SF samples. Multivariate analysis correlating intake water/SF characteristics with pesticide mineralization indicated that pesticide mineralization capacity depended on a range of intake water characteristics, but was not necessarily explained by the presence of the pesticide in the intake water and hence the in situ exposure of the SF community to the pesticide. This was supported by testing a sample from DWTP Kluizen for its capacity to mineralize 5 other pesticides including pesticides not present or occasionally present in the intake water. All of those pesticides were mineralized as well.

Effect of temperature, pH and total organic carbon variations on microbial turnover of 13C315N-glyphosate in agricultural soil

Glyphosate is the best-selling and the most-used broad-spectrum herbicide worldwide. Microbial conversion of glyphosate to CO2 and biogenic non-extractable residues (bioNER) leads to its complete degradation. The degradation of glyphosate may vary in different soils and it depends on environmental conditions and soil properties. To date, the influence of temperature, soil pH and total organic carbon (TOC) on microbial conversion of glyphosate to bioNER has not been investigated yet. The pH or TOC of an agricultural original soil (pH 6.6, TOC 2.1%) was modified using sulfuric acid or farmyard manure (FYM), respectively. Each treatment: original (I), 3% TOC (II), 4% TOC (III), pH 6.0 (IV) and pH 5.5 (V) was amended with 13C315N-glyphosate and incubated at 10 °C, 20 °C and 30 °C for 39 days. The temperature was the main factor controlling the mineralization and the extractable 13C315N-glyphosate, whereas higher TOC content and lower pH resulted in enhanced formation of 13C-bioNER. After 39 days the cumulative mineralization of 13C-glyphosate was in the range of 12-22% (10 °C), 37-47% (20 °C) and 43-54% (30 °C). Extractable residues of 13C-glyphosate were in the range of 10-21% (10 °C) and 4-10% (20 °C and 30 °C); whereas those of 15N-glyphosate were as follows 20-32% (10 °C) and 12-25% (20 °C and 30 °C). The 13C-NER comprised about 53-69% of 13C-mass balance in soils incubated at 10 °C, but 40-50% in soils incubated at 20 °C and 30 °C. The 15N-NER were higher than the 13C-NER and varied between 62% and 74% at 10 °C, between 53% and 81% at 20 °C and 30 °C. A major formation of 13C-bioNER (72-88% of 13C-NER) at 20 °C and 30 °C was noted in soil amended with FYM. An increased formation of 15N-bioNER (14-17% of 15N-NER) was also observed in FYM-amended soil. The xenobiotic 15N-NER had a major share within the 15N-NER and thus need to be considered when assessing the environmental risk of glyphosate-NER.

Soil microbial communities and glyphosate decay in soils with different herbicide application history

This study evaluates the glyphosate dissipation under field conditions in three types of soil, and aims to determine the importance of the following factors in the environmental persistence of herbicide: i) soil bacterial communities, ii) soil physicochemical properties, iii) previous exposure to the herbicide. A soil without previous record of GP application (P0) and two agricultural soils, with 5 and >10years of GP exposure (A5 and A10) were subjected to the application of glyphosate at doses of 3mg·kg-1. The concentration of GP and AMPA was determined over time and the dynamics of soil bacterial communities was evaluated using 16S ARN ribosomal gene amplicon-sequencing. The GP exposure history affected the rate but not the extent of GP biodegradation. The herbicide was degraded rapidly, but P0 soil showed a dissipation rate significantly lower than soils with agricultural history. In P0 soil, a significant increase in the relative abundance of Bacteroidetes was observed in response to herbicide application. More generally, all soils displayed shifts in bacterial community structure, which nevertheless could not be clearly associated to glyphosate dissipation, suggesting the presence of redundant bacteria populations of potential degraders. Yet the application of the herbicide prompted a partial disruption of the bacterial association network of unexposed soil. On the other hand, higher values of linear (Kd) and nonlinear (Kf) sorption coefficient in P0 point to the relevance of cation exchange capacity (CEC), clay and organic matter to the capacity of soil to adsorb the herbicide, suggesting that bioavailability was a key factor for the persistence of GP and AMPA. These results contribute to understand the relationship between bacterial taxa exposed to the herbicide, and the importance of soil properties as predictors of the possible rate of degradation and persistence of glyphosate in soil.

Herbicides in river water across the northeastern Italy: occurrence and spatial patterns of glyphosate, aminomethylphosphonic acid, and glufosinate ammonium

Glyphosate and glufosinate ammonium are the active ingredients of commonly used herbicides. Active agricultural lands extend over a large part of the Veneto region (Eastern Po Valley, Italy) and glyphosate and glufosinate ammonium are widely used. Consequently, surface waters can be potentially contaminated. This study investigates the occurrence of glyphosate and glufosinate ammonium as well as aminomethylphosphonic acid (AMPA, the degradation product of glyphosate) in river water of Veneto. Eighty-six samples were collected in 2015 at multiple sampling points across the region. Samples were analyzed for the two target herbicides, AMPA as well as for other variables, including water temperature, pH, dissolved oxygen, conductivity, hardness, BOD, COD, inorganic ions, total nitrogen, total phosphorus, total suspended solids, arsenic, and lead. The average concentrations (all samples) were 0.17, 0.18, and 0.10 μg L-1 for glyphosate, AMPA, and glufosinate ammonium, respectively. The European upper tolerable level for pesticides (annual average 0.1 μg L-1) was often exceeded. Chemometric analysis was therefore applied to (i) investigate the relationships among water pollutants, (ii) detect the potential sources of water contamination, (iii) assess the effective water pollution of rivers by identifying river basins with anomalous pollution levels, and (iv) assess the spatial variability of detected sources. Factor analysis identified four factors interpreted as potential sources and processes (use of herbicides, leaching of fertilizers, urban/industrial discharges, and the biological activity on polluted or stagnant waters). A discriminant analysis revealed that the pollution from anthropogenic discharges is homogeneously present in surface water of Veneto, while biological activity and fertilizers present heterogeneous distributions. This study gives insights into the concentrations of herbicides in rivers flowing through a wide region that has heavy use of these chemicals in agriculture. The study also points out some hot-spots and suggests the future implementation of the current monitoring protocols and network.

Large variation in glyphosate mineralization in 21 different agricultural soils explained by soil properties

Glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) have frequently been detected in surface water and groundwaters. Since adequate glyphosate mineralization in soil may reduce its losses to environment, improved understanding of site specific factors underlying pesticide mineralization in soils is needed. The aim of this study was to investigate the relationship between soil properties and glyphosate mineralization. To establish a sound basis for resilient correlations, the study was conducted with a large number of 21 agricultural soils, differing in a variety of soil parameters, such as soil texture, soil organic matter content, pH, exchangeable ions etc. The mineralization experiments were carried out with ¹⁴C labelled glyphosate at a soil water tension of -15 kPa and at a soil density of 1.3 g cm^-3 at 20 ± 1 °C for an incubation period of 32 days. The results showed that the mineralization of glyphosate in different agricultural soils varied to a great extent, from 7 to 70% of the amount initially applied. Glyphosate mineralization started immediately after application, the highest mineralization rates were observed within the first 4 days in most of the 21 soils. Multiple regression analysis revealed exchangeable acidity (H⁺ and Al³⁺), exchangeable Ca²⁺ ions and ammonium lactate extractable K to be the key soil parameters governing glyphosate mineralization in the examined soils. A highly significant negative correlation between mineralized glyphosate and NaOH-extractable residues (NaOH-ER) in soils strongly suggests that NaOH-ER could be used as a simple and reliable parameter for evaluating the glyphosate mineralization capacity. The NaOH-ER were composed of glyphosate, unknown ¹⁴C-residues, and AMPA (12%-65%, 3%-34%, 0%-11% of applied ¹⁴C, respectively). Our results highlighted the influential role of soil exchangeable acidity, which should therefore be considered in pesticide risk assessments and management to limit efficiently the environmental transfers of glyphosate.

Spatial glyphosate and AMPA redistribution on the soil surface driven by sediment transport processes - A flume experiment

This study investigates the influence of small-scale sediment transport on glyphosate and AMPA redistribution on the soil surface and on their off-site transport during water erosion events. Both a smooth surface (T1) and a surface with "seeding lines on the contour" (T2) were tested in a rainfall simulation experiment using soil flumes (1 × 0.5 m) with a 5% slope. A dose of 178 mg m-2 of a glyphosate-based formulation (CLINIC®) was applied on the upper 0.2 m of the flumes. Four 15-min rainfall events (RE) with 30-min interval in between and a total rainfall intensity of 30 mm h-1 were applied. Runoff samples were collected after each RE in a collector at the flume outlet. At the end of the four REs, soil and sediment samples were collected in the application area and in four 20 cm-segments downslope of the application area. Samples were collected according to the following visually distinguished soil surface groups: light sedimentation (LS), dark sedimentation (DS), background and aggregates. Results showed that runoff, suspended sediment and associated glyphosate and AMPA off-site transport were significantly lower in T2 than in T1. Glyphosate and AMPA off-site deposition was higher for T2 than for T1, and their contents on the soil surface decreased with increasing distance from the application area for all soil surface groups and in both treatments. The LS and DS groups presented the highest glyphosate and AMPA contents, but the background group contributed the most to the downslope off-site deposition. Glyphosate and AMPA off-target particle-bound transport was 9.4% (T1) and 17.8% (T2) of the applied amount, while water-dissolved transport was 2.8% (T1) and 0.5% (T2). Particle size and organic matter influenced the mobility of glyphosate and AMPA to off-target areas. These results indicate that the pollution risk of terrestrial and aquatic environments through runoff and deposition can be considerable.

Influence of dissolved organic matter on sorption and desorption of MCPA in ferralsol

MCPA (4-chloro-2-methylphenoxyacetic acid) is an acidic herbicide, widely used in paddy fields. The presence of dissolved organic matter (DOM) modifies the sorption-desorption of herbicides in soils. In this study, effects of DOM on sorption- desorption of MCPA were tested using three typical ferralsol soil types from China: rhodic ferralsol, haplic ferralsol and paddy soil. DOM preparations were extracted from the paddy soil (DOM_P), from a compost mixture of cassava stems with chicken manure (DOM_C), and from rice straw (DOM_R). Sorption-desorption of MCPA in the tested soil types was shown to follow pseudo first-order kinetics, and the calculated isotherm data fitted well with a Freundlich equilibrium model in the range of the studied concentrations. MCPA was weakly sorbed by the soils, producing low Freundlich coefficient values (K_f) (0.854 to 4.237). The presence of DOM reduced the K_f whereby DOM_C had the strongest and DOM_R the weakest effect. Presence of DOM also promoted MCPA desorption from the soils, again with DOM_C having the strongest effect and DOM_R the weakest. DOM coating changed the soil particle surface, as demonstrated by electron microscopy, and DOM also directly interacted with MCPA, as shown by Fourier-transform infrared spectroscopy. The experimental data were interpreted to suggest a competing sorption of DOM to ferralsol and an increased solubility of MCPA in the presence of DOM. The results indicate that the environmental risk of MCPA leaching to groundwater and surface flow is increased by presence of DOM, for instance as a result of organic fertilizer use.

Sorption and desorption of glyphosate, MCPA and tetracycline and their mixtures in soil as influenced by phosphate

Phosphate fertilizers and herbicides such as glyphosate and MCPA are commonly applied to agricultural land, and antibiotics such as tetracycline have been detected in soils following the application of livestock manures and biosolids to agricultural land. Utilizing a range of batch equilibrium experiments, this research examined the competitive sorption interactions of these chemicals in soil. Soil samples (0-15 cm) collected from long-term experimental plots contained Olsen P concentrations in the typical (13 to 20 mg kg-1) and elevated (81 to 99 mg kg-1) range of build-up phosphate in agricultural soils. The elevated Olsen P concentrations in field soils significantly reduced glyphosate sorption up to 50%, but had no significant impact on MCPA and tetracycline sorption. Fresh phosphate additions in the laboratory, introduced to soil prior to, or at the same time with the other chemical applications, had a greater impact on reducing glyphosate sorption (up to 45%) than on reducing tetracycline (up to 13%) and MCPA (up to 8%) sorption. The impact of fresh phosphate additions on the desorption of these three chemicals was also statistically significant, but numerically very small namely < 1% for glyphosate and tetracycline and 3% for MCPA. The presence of MCPA significantly reduced sorption and increased desorption of glyphosate, but only when MCPA was present at concentrations much greater than environmentally relevant and there was no phosphate added to the MCPA solution. Tetracycline addition had no significant effect on glyphosate sorption and desorption in soil. For the four chemicals studied, we conclude that when mixtures of phosphate, herbicides and antibiotics are present in soil, the greatest influence of their competitive interactions is phosphate decreasing glyphosate sorption and the presence of phosphate in solution lessens the potential impact of MCPA on glyphosate sorption. The presence of chemical mixtures in soil solution has an overall greater impact on the sorption than desorption of individual organic chemicals in soil.

Hydrogeological characteristics influencing the occurrence of pesticides and pesticide metabolites in groundwater across the Republic of Ireland

Pesticide contamination of water is a potential environmental issue which may impact the quality of drinking water. The full extent of pesticide contamination is not fully understood due to complex fate pathways in the subsurface. Groundwater pesticide occurrence was investigated at seven agricultural sites in different hydrogeological settings to identify where pesticide occurrence dominated in temperate maritime climatic conditions. In Ireland, six cereal dominated sites in the South East and one grassland site in the West were investigated. Soil and subsoils varied from acid brown earths with high permeability to clay and silt rich tills with lower permeability. Over a 2year monitoring period, 730 samples were collected from a network of dedicated wells and springs across the seven sites. Multi-nested piezometers were installed in intergranular, fissured and karstic type aquifers to target shallow, transition and deeper groundwaters. Several springs were also sampled and the network included a confined aquifer. Groundwater was analysed for nine pesticide active ingredients and eight metabolites. Mecoprop and 2,4-D were the most frequently detected active ingredients above the instrument detection limit, accounting for 36% and 26% of the 730 samples collected and analysed. Phenoxyacetic acid was the most frequently detected and widespread metabolite found in 39% of samples collected at all seven sites. Where the European Union drinking water standard of 0.1μg/L was exceeded, metabolites accounted for the majority of exceedances with 3,5-dichlorobenzoic acid (DBA) and phenoxyacetic acid (PAC) dominating. Highest detections were encountered in sites with well drained soils underlain by gravel and limestone aquifers and within gravel lenses in lower permeability subsoil. Across the seven sites pesticide detections were mostly associated with metabolites and the environmental impact of many of these is unknown as they have received little attention in groundwater previously.

Sorption and desorption of glyphosate in Mollisols and Ultisols soils of Argentina

In Argentina, glyphosate use has increased exponentially in recent years as a result of the widespread adoption of no-till management combined with genetically modified glyphosate-resistant crops. This massive use of glyphosate has created concern about its potential environmental impact. Sorption-desorption of glyphosate was studied in 3 Argentinean soils with contrasting characteristics. Glyphosate sorption isotherms were modeled using the Freundlich equation to estimate the sorption coefficient (Kf ). Glyphosate sorption was high, and the Kf varied from 115.6 to 1612 mg1-1/n L1/n /kg. Cerro Azul soil had the highest glyphosate sorption capacity as a result of a combination of factors such as higher clay content, cation exchange capacity, total iron, and aluminum oxides, and lower available phosphorus and pH. Desorption isotherms were also modeled using the Freundlich equation. In general, desorption was very low (<12%). The low values of hysteresis coefficient confirm that glyphosate strongly sorbs to the soils and that it is almost an irreversible process. Anguil soil had a significantly higher desorption coefficient (Kfd ) than the other soils, associated with its lower clay content and higher pH and phosphorus. Glyphosate high sorption and low desorption to the studied soils may prevent groundwater contamination. However, it may also affect its bioavailability, increasing its persistence and favoring its accumulation in the environment. The results of the present study contribute to the knowledge and characterization of glyphosate retention in different soils. Environ Toxicol Chem 2017;36:2587-2592. © 2017 SETAC.

Behaviour of glyphosate in a reservoir and the surrounding agricultural soils

Glyphosate (GPS) is an herbicide currently used on olive crops in Spain, and can be transported to the nearby reservoirs currently used for human consumption. The purpose of this work was to study the behaviour and environmental fate of GPS in water and sediments of the Vibora Reservoir, its tributary river, and the surrounding agricultural soils to assess the risk of water pollution of this reservoir. The adsorption of GPS by different matrices was as follows: heading of the reservoir sediment (Cabecera)>tail sediment (Cola)>soils>Vibora sediment. The highest amount of oxides (especially Fe oxides) was observed in sediments from Cabecera and Cola whereas the lowest values were recorded on Vibora sediment. Results indicate that the highest GPS adsorption is due to the amorphous oxides and the edge sites of the clay minerals. Glyphosate adsorption increased with decreasing pH from 8 to 7. The desorption percentage of GPS from the four soils studied ranged only from 0.40 to 1.22%. Desorption was almost irreversible for Cabecera and Cola sediments, with values between 0 and 1.1%. Conversely, Vibora sediment presented about 20% desorption, probably due to its coarse texture and lower levels of amorphous oxides. Hockey-stick first-order kinetics was the best descriptor for water glyphosate dissipation at the Cabecera and Cola locations, and simple first-order kinetic for the water from the tributary Vibora River. The half-lives (DT50) were between 6.3 and 11.0days. The rapid degradation of GPS in surface waters and its practically irreversible sorption on these soils and sediments implies that GPS use in similar agricultural areas is of very low environmental risk. This manuscript also outlines the importance of the presence of photo-sensitizers in waters in the degradation routes of GPS in reservoirs.

Phenoxy herbicide removal from aqueous solutions using fast pyrolysis switchgrass biochar

The release of herbicides is known to negatively impact humans and the environment. We report the use of a low cost biochar (prepared through fast pyrolysis) to successfully remove phenoxy herbicides from aqueous solutions. The biochar was characterized using: FT-IR, SEM, pH_pzc, elemental analysis, and surface area measurements. Sorption experiments were run at pH values from 2 to 10, adsorbate concentrations from 25 to 300 mg/L and temperatures from 25 to 45 °C. Adsorption isotherms were evaluated from 25 to 45 °C using both two parameter (Freundlich and Langmuir) and three parameter (Redlich-Peterson and Toth) adsorption isotherm models. The maximum adsorption capacities for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) were Q⁰_SGB∼134 mg/g and Q⁰_SGB∼50 mg/g, respectively, at pH 2. This low surface area switchgrass biochar (1.1 m²/g) can adsorb far more MCPA per unit of measured surface area (45 mg/m²) than high surface area commercial activated carbons (1050-1150 m²/g) which absorb only 0.08-0.11 mg/m², and are also expensive. This indicates that biochar three dimensional swelling occurs in an aqueous environment and adsorbates are imbibed and adsorbed at additional sorption sites.

Conservative tracer bromide inhibits pesticide mineralisation in soil

Bromide is a conservative tracer that is often applied with non-conservative solutes such as pesticides to estimate their retardation in the soil. It has been applied in concentrations of up to 250 g Br L-1, levels at which the growth of single-celled organisms can be inhibited. Bromide applications may therefore affect the biodegradation of non-conservative solutes in soil. The present study investigated the effect of potassium bromide (KBr) on the mineralisation of three pesticides - glyphosate, MCPA and metribuzin - in four agricultural A-horizon soils. KBr was added to soil microcosms at concentrations of 0, 0.5, 2.5 and 5 g Br- L-1 in the soil solution. The study concluded that KBr had a negative effect on pesticide mineralisation. The inhibitory effect varied depending on the KBr concentration, the type of pesticide and the type of soil. Furthermore, 16 S amplicon sequencing revealed that the KBr treatment generally reduced the abundance of bacteroidetes and proteobacteria on both an RNA and DNA level. Therefore, in order to reduce the effect of KBr on the soil bacterial community and consequently also on xenobiotic degradation, it is recommended that KBr be applied in a concentration that does not exceed 0.5 g Br- L-1 in the soil water.

Phosphate fertilizer impacts on glyphosate sorption by soil

This research examined the impact of field-aged phosphate and cadmium (Cd) concentrations, and fresh phosphate co-applications, on glyphosate sorption by soil. Soil samples were collected in 2013 from research plots that had received, from 2002 to 2009, annual applications of mono ammonium phosphate (MAP) at 20, 40 and 80 kg P ha(-1) and from products containing 0.4, 70 or 210 mg Cd kg(-1) as an impurity. A series of batch equilibrium experiments were carried out to quantify the glyphosate sorption distribution constant, Kd. Extractable Cd concentrations in soil had no significant effect on glyphosate sorption. Glyphosate Kd values significantly decreased with increasing Olsen-P concentrations in soil, regardless of the pH conditions studied. Experiments repeated with a commercially available glyphosate formulation showed statistically similar results as the experiments performed with analytical-grade glyphosate. Co-applications of MAP with glyphosate also reduced the available sorption sites to retain glyphosate, but less so when soils already contain large amounts of phosphate. Glyphosate Kd values in soils ranged from 173 to 939 L kg(-1) under very strong to strongly acidic condition but the Kd was always <100 L kg(-1) under moderately acidic to slightly alkaline conditions. The highest Olsen-P concentrations in soil reduced Kd values by 25-44% relative to control soils suggesting that, under moderately acidic to slightly alkaline conditions, glyphosate may become mobile by water in soils with high phosphate levels. Otherwise, glyphosate residues in agricultural soils are more likely to be transported off-site by wind and water-eroded sediments than by leaching or runoff.

Adsorption and degradation of phenoxyalkanoic acid herbicides in soils: A review

The primary aim of the present review on phenoxyalkanoic acid herbicides-2-(2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chloro-2-methylphenoxy) acetic acid (MCPA), (2R)-2-(2,4-dichlorophenoxy) propanoic acid (dichlorprop-P), (2R)-2-(4-chloro-2-methylphenoxy) propanoic acid (mecoprop-P), 4-(2,4-dichlorophenoxy) butanoic acid (2,4-DB), and 4-(4-chloro-2-methylphenoxy) butanoic acid (MCPB)-was to compare the extent of their adsorption in soils and degradation rates to assess their potential for groundwater contamination. The authors found that adsorption decreased in the sequence of 2,4-DB > 2,4-D > MCPA > dichlorprop-P > mecoprop-P. Herbicides are predominantly adsorbed as anions-on organic matter and through a water-bridging mechanism with adsorbed Fe cations-and their neutral forms are adsorbed mainly on organic matter. Adsorption of anions of 2,4-D, MCPA, dichlorprop-P, and mecoprop-P is inversely correlated with their lipophilicity values, and modeling of adsorption of the compounds based on this relationship is possible. The predominant dissipation mechanism of herbicides in soils is bacterial degradation. The contribution of other mechanisms, such as degradation by fungi, photodegradation, or volatilization from soils, is much smaller. The rate of bacterial degradation decreased in the following order: 2,4-D > MCPA > mecoprop-P > dichlorprop-P. It was found that 2,4-D and MCPA have the lowest potential for leaching into groundwater and that mecoprop-P and dichlorprop-P have slightly higher potential. Because of limited data on adsorption and degradation of 2,4-DB and MCPB, estimation of their leaching potential was not possible.

Adsorption and characterization of MCPA on DDTMA- and raw-montmorillonite: Surface sites involved

The 4-chloro-2-methylphenoxy acid (MCPA) is an herbicide widely used in agriculture, which generates a great concern about contamination of surface water and serious consequences for human health and the environment. In this work, the adsorption of MCPA on an Argentine montmorillonite (MMT) and its organo-montmorillonite product (OMMT) with different dodecyl trimethyl ammonium loading was investigated. MCPA adsorption on OMMT increases at least 3 times, with respect to the amount determined for MMT. X-ray diffraction and zeta potential analyses indicated the inner (interlayer) and outer surface participate as adsorption sites. Changes in surface electric charge and also interlayer expansion suggest that dimethyl amine (MCPA counterion) was also surface-adsorbed. The larger aggregates of OMMT, without and with MCPA, obtained compared to those of MMT samples, generate an improvement in the coagulation efficiency. This property, particularly after MCPA retention, allows an easier separation of the solids from the solution and enables a simple technological process application.

Influence of substrate water saturation on pesticide dissipation in constructed wetlands

Constructed wetlands are an effective and practical option for removing pesticide pollution from runoff or subsurface drainage water. The objective of this study was to assess the efficiencies of a ditch with a bundle of straw placed in its centre and a vegetated pond installed in grass cover bands at downstream of a drained plot. The dissipation rates of three herbicides and three fungicides were monitored on four substrates commonly found in constructed wetlands (two soils, sediment and straw). The influence of water content was determined in a sequence of three steps (flooded-unsaturated-flooded) over 120 days. The pesticide dissipation rates observed during the 120 days of incubation ranged from 1.4 to 100%. Isoproturon and 2,4-MCPA (MCPA) showed the highest dissipation rates, which ranged from 61.0 to 100% of the applied quantities during the 120 days of incubation. In contrast, boscalid and tebuconazole showed the lowest dissipation rates, which ranged from 1.4 to 43.9% of the applied quantities during the 120 days of incubation. The estimated DT50 values ranged from 20.5 days to more than 1 year and were influenced by the substrate water content. The soil and straw substrates had the lowest DT50 values during the unsaturated conditions, whereas the sediments had the lowest DT50 values during the flooded conditions. These results could be explained by an adaptation of microbial communities to their environmental conditions. Thus, the most favourable conditions of dissipation for soils and straw are observable when the drainage ceases (spring and summer). However, favourable conditions occur all year for the sediments, except when the constructed wetlands are dry. The results suggest that the dissipation of pesticides in constructed wetlands contributes to the long-term effectiveness of these buffer zones for reducing water pollution.

Urea Fertilizer and pH Influence on Sorption Process of Flumetsulam and MCPA Acidic Herbicides in a Volcanic Soil

The aim of this study was to evaluate the influence of urea fertilizer and pH on the sorption process of two acidic herbicides, flumetsulam (2',6'-difluoro-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonanilide) and MCPA (4-chloro--tolyloxyacetic acid), on an Andisol. Urea reduced the adsorption of MCPA but not that of flumetsulam. The Freundlich parameter of MCPA decreased from 8.5 to 5.1 mg L kg. This finding could be attributed to an increase in dissolved organic C due to an initial increase in soil pH for urea application. The higher acidic character of MCPA compared with that of flumetsulam produced a greater hydrolysis of urea, leading to a further pH increase. A marked effect of pH on the adsorption of both herbicides was observed. The organic C distribution coefficient () values for flumetsulam were in the range of 74 to 10 L kg, while those of MCPA were in the range of 208 to 45 L kg. In the kinetic studies, the pseudo-second-order model appeared to fit the data best ( > 0.994). The initial adsorption rates () ranged from 20.00 to 4.59 mg kg h for flumetsulam and from 125.00 to 25.60 mg kg hfor MCPA. Both herbicides were adsorbed rapidly during the first stage of the sorption process, and the rates of sorption were dependent on pH. The application of the Elovich and Weber-Morris models led us to conclude that mass transfer through the boundary layer and, to a lesser degree, intraparticle diffusion were influenced by the chemical character of the herbicide. These results suggest that urea application could increase leaching of acid herbicides in soils.

Decay characteristics and erosion-related transport of glyphosate in Chinese loess soil under field conditions

The decay characteristics and erosion-related transport of glyphosate and aminomethylphosphonic acid (AMPA) were monitored for 35 d at different slope gradients and rates of application in plots with loess soil on the Loess Plateau, China. The initial glyphosate decayed rapidly (half-life of 3.5d) in the upper 2 cm of soil following a first-order rate of decay. AMPA content in the 0-2 cm soil layer correspondingly peaked 3d after glyphosate application and then gradually decreased. The residues of glyphosate and AMPA decreased significantly with soil depth (p<0.05) independently of the slope inclination and application rate. About 0.36% of the glyphosate initially applied was transported from plots after one erosive rain 2d after the application. Glyphosate and AMPA concentrations in runoff were low while the contents in the sediment were much higher than in the upper 2 cm of the soil.

CAPSULE

Although the rate of glyphosate decay is rapid in Chinese loess soil, the risks of glyphosate and AMPA need to be taken into account especially in the area with highly erosive rainfall.

Short-term transport of glyphosate with erosion in Chinese loess soil--a flume experiment

Repeated applications of glyphosate may contaminate the soil and water and threaten their quality both within the environmental system and beyond it through water erosion related processes and leaching. In this study, we focused on the transport of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) related to soil erosion at two slope gradients (10 and 20°), two rates of pesticide with a formulation of glyphosate (Roundup®) application (360 and 720 mg m(-2)), and a rain intensity of 1.0 mm min(-1) for 1 h on bare soil in hydraulic flumes. Runoff and erosion rate were significantly different within slope gradients (p<0.05) while suspended load concentration was relatively constant after 15 min of rainfall. The glyphosate and AMPA concentration in the runoff and suspended load gradually decreased. Significant power and exponent function relationship were observed between rainfall duration and the concentration of glyphosate and AMPA (p<0.01) in runoff and suspended load, respectively. Meanwhile, glyphosate and AMPA content in the eroded material depended more on the initial rate of application than on the slope gradients. The transport rate of glyphosate by runoff and suspended load was approximately 14% of the applied amount, and the chemicals were mainly transported in the suspended load. The glyphosate and AMPA content in the flume soil at the end of the experiment decreased significantly with depth (p<0.05), and approximately 72, 2, and 3% of the applied glyphosate (including AMPA) remained in the 0-2, 2-5, and 5-10 cm soil layers, respectively. The risk of contamination in deep soil and the groundwater was thus low, but 5% of the initial application did reach the 2-10 cm soil layer. The risk of contamination of surface water through runoff and sedimentation, however, can be considerable, especially in regions where rain-induced soil erosion is common.

The potential for bioaugmentation of sand filter materials from waterworks using bacterial cultures degrading 4-chloro-2-methylphenoxyacetic acid

BACKGROUND

The herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) is found frequently in Danish groundwater in concentrations exceeding the EU threshold limit of 0.1 µg L(-1) . Groundwater is used for drinking water, and one potential remediation strategy is bioaugmentation using inoculation of sand filters at affected waterworks with degrader bacteria. Numerous bacteria degrading phenoxyacetic acid herbicide have previously been isolated, and they may be candidates for bioaugmentation processes. Designing the optimum inoculum, however, requires knowledge of the capacity for degrading realistically low herbicide concentrations and the robustness of the bacteria when inoculated into sand filter materials.

RESULTS

Testing a range of different MCPA-mineralising bacterial combinations, using a high-throughput microplate radiorespirometric mineralisation assay, highlighted three efficient cocultures for mineralising low MCPA concentrations. Cocultures demonstrating a shorter time delay before initiation of (14) C-ring-labelled MCPA mineralisation to (14) CO2 , and a more extensive mineralisation of MCPA, compared with those of single strains, were found. When inoculated into different sand filter materials, the coculture effect was diminished, but several single strains enhanced MCPA mineralisation significantly at low MCPA concentrations.

CONCLUSION

This study shows that an increase in the potential for mineralisation of low herbicide concentrations in sand filter materials can be achieved by inoculating with bacterial degrader cultures. © 2014 Society of Chemical Industry.

Bioremediation potential of glyphosate-degrading Pseudomonas spp. strains isolated from contaminated soil

Bacterial strains capable of utilizing glyphosate as the sole carbon source were isolated from contaminated soil by the enrichment culture method and identified based on partial 16S rRNA gene sequence analysis. Pseudomonas spp. strains GA07, GA09 and GC04 demonstrated the best degradation capabilities towards glyphosate and were used for the laboratory experiments of glyphosate bioremediation. Inoculating glyphosate-treated soil samples with these three strains resulted in a 2-3 times higher rate of glyphosate removal than that in non-inoculated soil. The degradation kinetics was found to follow a first-order model with regression values greater than 0.96. Cell numbers of the introduced bacteria decreased from 4.4 × 10(6) CFU/g to 3.4-6.7 × 10(5) CFU/g dry soil within 18 days of inoculation. Due to the intense degradation of glyphosate, the total dehydrogenase activity of the soil microbial community increased by 21.2-25.6%. Analysis of glyphosate degradation products in cell-free extracts showed that glyphosate breakdown in strain GA09 was catalyzed both by C-P lyase and glyphosate oxidoreductase. Strains GA07 and GC04 degraded glyphosate only via glyphosate oxidoreductase, but no further metabolite was detected. These results highlight the potential of the isolated bacteria to be used in the bioremediation of GP-contaminated soils.

Effect of soil aeration and phosphate addition on the microbial bioavailability of carbon-14-glyphosate

The adsorption, desorption, degradation, and mineralization of C-glyphosate [-(phosphonomethyl)glycine] were examined in Catlin (a fine-silty, mixed, superactive, mesic Oxyaquic Argiudoll), Flanagan (a fine, smectitic, mesic Aquic Argiudoll), and Drummer (a fine-silty, mixed, superactive, mesic Typic Endoaquoll) soils under oxic and anoxic soil conditions. With the exception of the Drummer soil, soil aeration did not significantly alter the adsorption pattern of C-glyphosate to soils. Herbicide desorption was generally enhanced with anaerobiosis in all the soil types. Anoxic soils demonstrated slower microbial degradation and mineralization kinetics of C-glyphosate than oxic soils in all the soil types studied. Phosphate additions significantly reduced the adsorption of C-glyphosate to soils irrespective of soil aeration and confirmed the well-established competitive adsorption theory. The addition of soil phosphate stimulated degradation only in anoxic soils. The results from this research highlight the importance of soil redox conditions as an important factor affecting the bioavailability and mobility of glyphosate in soils.

Kinetics and isotherm analysis of 2,4-dichlorophenoxyl acetic acid adsorption onto soil components under oxic and anoxic conditions

2,4-dichlorophenoxyl acetic acid (2,4-D, pKa = 2.8) is used extensively as a herbicide in agricultural practices. Its sorption behavior on both untreated and soils treated to significantly remove specific components (organic and iron and manganese [Fe-Mn] oxides and hydroxides phases) was investigated under oxic and anoxic conditions. The chemical and structural heterogeneity of the soil components were characterized by elemental analysis and X-ray diffraction (XRD). The coexistence of the various components seems to either mask sorption sites on the untreated soil surfaces or inhibit interlayer diffusion of 2,4-D. All sorption data conform to the Freundlich description and a pseudo-second-order kinetic model. There was a strong positive correlation between sorption capacity K(d), and surface area (r(2) ≤ 0.704), but a negative correlation was uncovered with both pH and organic carbon (r(2) ≤ -0.860). The results indicate that 2,4-D is preferably sorbed under oxic rather than anoxic conditions and it is greater on soils containing a high Fe content. There was incomplete 2,4-D sorption reversibility, with desorption occurring more rapidly under anoxic conditions. The study suggests that stimulation of Fe III reduction could be used for the bioremediation of a 2,4-D-contaminated site.

Pesticide occurrence in groundwater and the physical characteristics in association with these detections in Ireland

This study explores the associations of pesticide occurrence in groundwater to geological characteristics of the monitoring points (MPs) contributing area. Pesticide analyses were undertaken during a 2-year groundwater monitoring campaign which generated 845 samples. MCPA and mecoprop were the most frequently detected pesticides in groundwater. Each MP (n = 158) had a specifically delineated zone of contribution (ZOC) and the dominant physical characteristics present from nine national datasets were recorded for each ZOC. Associations between detections in groundwater and the dominant physical characteristic in each MPs ZOC tested were then statistically analyzed using Fisher's exact test, logistic regression, and multiple logistic regression. The original physical characteristic datasets used that were associated with detections in groundwater were the type of MP, aquifer type, and Quaternary deposit type. Logistic regression revealed that springs, regionally important aquifer types, aquifers with a karstic flow regime, and alkaline Quaternary deposits in existence above karst aquifers in a MP's ZOC were more likely to have a pesticide detection in groundwater. Multiple regression from this exploratory work showed some mutual dependency between soil association, aquifer type, and the Geological Survey of Ireland groundwater vulnerability map. The combination of national monitoring data and physical attribute datasets can be used to explore key areas where groundwater is more vulnerable to pesticide contamination.

Sorption-desorption and biosorption of bisphenol A, triclosan, and 17α-ethinylestradiol to sewage sludge

To better understand the fate of microconstituents (MCs) in an activated sludge (AS) system, sorption, biosorption, and desorption studies were investigated at μg/L range for 17α-ethinylestradiol (EE2), bisphenol A (BPA), and triclosan (TCS). Batch experiments with activated and deactivated sludge originating from continuous flow porous pot reactors operating at solid retention times (SRTs) of 5, 10, and 15 days were conducted in order to investigate the sorption kinetics and distinguish physicochemical sorption and biosorption. The effect of SRT and the biomass concentration on sorption kinetics were also studied. Selected MCs showed high sorption affinity to the non-viable biomass during the first 30 min of the experiment, which was gradually reduced until equilibrium was reached. Desorption results showed two distinct stages, a very rapid desorption within 20 min followed by a slow desorption stage. Biosorption study indicated that the soluble concentrations of target compounds decreased rapidly for selected MCs similar to the sorption study; however, the soluble and solid phase concentrations continued to decrease slowly during the length of the experiment which indicates the possible biodegradation of these compounds in both phases. Finally, mathematical models were applied to describe the sorption mechanism and Freundlich sorption isotherms with values of 1/n close to 1 were found to best fit the results which demonstrate that all tested concentrations result on the linear part of the Freundlich isotherm. Calculation of the Freundlich constant, KF and distribution coefficient, Kd exhibited the greater tendency of EE2 and TCS for sorption, compared to BPA. The results of this study indicated that the SRT had a clear effect on the sorption kinetics where the highest sorption rate constant was achieved for a SRT of 10 days for all three target substances. This could be due to change of the morphology of the biomass from reactors operating at different SRTs.

Carbon-14-glyphosate behavior in relationship to pedoclimatic conditions and crop sequence

The recognition of glyphosate [(-phosphonomethyl) glycine] behavioral patterns can be readily examined using a pedoclimatic gradient. In the present study, glyphosate adsorption-desorption and degradation were examined under different scenarios in relationship to soil properties and soil use applications. Three sites with varied pedoclimatic conditions and two crop sequences were selected. Adsorption-desorption and glyphosate distribution in mineralized, extractable, and nonextractable fractions were assessed under laboratory conditions. Glyphosate sorption was characterized by isotherms and glyphosate degradation using the distribution of C-glyphosate radioactivity among mineralized fractions, two extractable fractions (in water, ER1; in NHOH, ER2), and nonextractable fractions. Results showed sorption indices (distribution coefficient and Freundlich sorption coefficient : 13.4 ± 0.3-64.1 ± 0.9 L kg and 16.2-60.6, respectively), and hysteresis increased among soil sites associated with decreasing soil particle size <2 μm, soil organic matter, and other soil properties associated with soil granulometry. A multiple stepwise regression analysis was applied to estimate the relationship between values and soil properties. Cation exchange capacity, water field capacity, and Bray-1 P were the soil properties retained in the equation. Soils under continuous soybean [ (L.) Merr.] (monoculture) treatment exhibited reduced glyphosate adsorption and decreased hysteresis desorption relative to soils under rotation. To our knowledge, these results are the first to demonstrate that soils with identical properties exhibited different glyphosate retention capacities based on crop sequence. We propose possible explanations for this observation. Our results suggested that characterization of the variability in soil property gradients can serve to determine glyphosate behavioral patterns, which can establish a criterion for use in reducing potential environmental risks.

Does microbial centimeter-scale heterogeneity impact MCPA degradation in and leaching from a loamy agricultural soil?

The potential for pesticide degradation varies greatly at the centimeter-scale in agricultural soil. Three dimensional numerical simulations were conducted to evaluate how such small-scale spatial heterogeneity may affect the leaching of the biodegradable pesticide 2-methyl-4-chlorophenoxyacetic acid (MCPA) in the upper meter of a variably-saturated, loamy soil profile. To incorporate realistic spatial variation in degradation potential, we used data from a site where 420 mineralization curves over 5 depths have been measured. Monod kinetics was fitted to the individual curves to derive initial degrader biomass values, which were incorporated in a reactive transport model to simulate heterogeneous biodegradation. Six scenarios were set up using COMSOL Multiphysics to evaluate the difference between models having different degrader biomass distributions (homogeneous, heterogeneous, or no biomass) and either matrix flow or preferential flow through a soil matrix with a wormhole. MCPA leached, within 250 days, below 1m only when degrader biomass was absent and preferential flow occurred. Both biodegradation in the plow layer and the microbially active lining of the wormhole contributed to reducing MCPA-leaching below 1m. The spatial distribution of initial degrader biomass within each soil matrix layer, however, had little effect on the overall MCPA-leaching.

Is biological treatment a viable alternative for micropollutant removal in drinking water treatment processes?

In western societies, clean and safe drinking water is often taken for granted, but there are threats to drinking water resources that should not be underestimated. Contamination of drinking water sources by anthropogenic chemicals is one threat that is particularly widespread in industrialized nations. Recently, a significant amount of attention has been given to the occurrence of micropollutants in the urban water cycle. Micropollutants are bioactive and/or persistent chemicals originating from diverse sources that are frequently detected in water resources in the pg/L to μg/L range. The aim of this review is to critically evaluate the viability of biological treatment processes as a means to remove micropollutants from drinking water resources. We first place the micropollutant problem in context by providing a comprehensive summary of the reported occurrence of micropollutants in raw water used directly for drinking water production and in finished drinking water. We then present a critical discussion on conventional and advanced drinking water treatment processes and their contribution to micropollutant removal. Finally, we propose biological treatment and bioaugmentation as a potential targeted, cost-effective, and sustainable alternative to existing processes while critically examining the technical limitations and scientific challenges that need to be addressed prior to implementation. This review will serve as a valuable source of data and literature for water utilities, water researchers, policy makers, and environmental consultants. Meanwhile this review will open the door to meaningful discussion on the feasibility and application of biological treatment and bioaugmentation in drinking water treatment processes to protect the public from exposure to micropollutants.

Reduced leaching of the herbicide MCPA after bioaugmentation with a formulated and stored Sphingobium sp

The use of pesticides on sandy soils and on many non-agricultural areas entails a potentially high risk of water contamination. This study examined leaching of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) after bioaugmentation in sand with differently formulated and stored Sphingobium sp. T51 and at different soil moisture contents. Dry formulations of Sphingobium sp. T51 were achieved by either freeze drying or fluidised bed drying, with high initial cell viability of 67-85 %. Storage stability of T51 cells was related to formulation excipient/carrier and storage conditions. Bacterial viability in the fluidised bed-dried formulations stored at 25 °C under non-vacuum conditions was poor, with losses of at least 97 % within a month. The freeze-dried formulations could be stored substantially longer, with cell survival rates of 50 %, after 6 months of storage at the same temperature under partial vacuum. Formulated and long-term stored Sphingobium cells maintained their MCPA degradation efficacy and reduced MCPA leaching as efficiently as freshly cultivated cells, by at least 73 % when equal amounts of viable cells were used. The importance of soil moisture for practical field bioaugmentation techniques is discussed.

Centimeter-scale spatial variability in 2-methyl-4-chlorophenoxyacetic Acid mineralization increases with depth in agricultural soil

Mineralization of organic chemicals in soil is typically studied using large homogenized samples, but little is known about the small-scale spatial distribution of mineralization potential. We studied centimeter-scale spatial distribution of 2-methyl-4-chlorophenoxyacetic acid (MCPA) mineralization activity at different depths (8-115 cm) in a Danish agricultural soil profile using a 96-well microplate C-radiorespirometric method for small-volume samples. The heterotrophic microbial population and specific MCPA degraders decreased 10- to 100-fold from the plow layer to a depth of 115 cm. MCPA was mineralized in all samples in the plow layer, but only about 60% in the transition zone immediately below the plow layer showed mineralization; at greater depth even fewer samples showed mineralization. A patchy spatial distribution of mineralization activity was observed from right below the plow layer and in the subsoil, with a few clearly defined active zones surrounded by areas devoid of mineralization activity. Due to the patchy distribution of mineralization activity at the centimeter scale just beneath the plow layer, MCPA and presumably other weakly sorbing pesticides might be at risk of leaching to the groundwater if transported from the plow layer into the subsoil.

Influence of herbicide glyphosate on growth and aflatoxin B1 production by Aspergillus section Flavi strains isolated from soil on in vitro assay

The effect of six glyphosate concentrations on growth rate and aflatoxin B1 (AFB1) production by Aspergillus section Flavi strains under different water activity (aW) on maize-based medium was investigated. In general, the lag phase decreased as glyphosate concentration increased and all the strains showed the same behavior at the different conditions tested. The glyphosate increased significantly the growth of all Aspergillus section Flavi strains in different percentages with respect to control depending on pesticide concentration. At 5.0 and 10 mM this fact was more evident; however significant differences between both concentrations were not observed in most strains. Aflatoxin B1 production did not show noticeable differences among different pesticide concentrations assayed at all aW in both strains. This study has shown that these Aspergillus flavus and A. parasiticus strains are able to grow effectively and produce aflatoxins in high nutrient status media over a range of glyphosate concentrations under different water activity conditions.

Phenoxyalkanoic acid herbicide sorption and the effect of co-application in a Haplic Cambisol with contrasting management

The adsorption and desorption behaviour of two phenoxyalkanoic acid herbicides (MCPA and mecoprop-p) in a Haplic Cambisol with tillage and grassland management was examined using a batch equilibrium method. Additionally, the effect on adsorption of the simultaneous presence of the two herbicides was also studied. The sorption equilibrium was reached within 24h for adsorption and desorption in both soils. The experimental sorption data for MCPA and mecoprop-p fitted the Freundlich and the linear adsorption isotherms very well (R(2)>0.99). The Freundlich exponent values of the adsorption isotherm ranged from 0.91 to 0.98 indicating a non-linear and a linear adsorption of the two chemicals studied. Generally, mecoprop-p showed lower adsorption than MCPA, although the adsorption of both phenoxyalkanoic acid herbicides was low. The adsorption process was not fully reversed during one washing cycle, as the K(f) values for desorption were greater than corresponding K(f) values for adsorption. The Freundlich exponent (1/n) of the MCPA adsorption isotherm was affected by the simultaneous presence of both herbicides and tended more towards non-linearity, whilst the mecoprop-p adsorption exponent remained unaltered. The Freundlich and the linear adsorption coefficients calculated in the mix study were not that different from the adsorption coefficients calculated in the single compound study, and therefore single compound adsorption data can be used when modelling the fate of simultaneously applied phenoxyalkanoic acid herbicides. The study also indicated that both herbicides were poorly sorbed by the soils studied, and therefore may pose a risk of surface and/or groundwater pollution in Ireland.

Comparing metabolic functionalities, community structures, and dynamics of herbicide-degrading communities cultivated with different substrate concentrations

Two 4-chloro-2-methylphenoxyacetic acid (MCPA)-degrading enrichment cultures selected from an aquifer on low (0.1 mg liter(-1)) or high (25 mg liter(-1)) MCPA concentrations were compared in terms of metabolic activity, community composition, population growth, and single cell physiology. Different community compositions and major shifts in community structure following exposure to different MCPA concentrations were observed using both 16S rRNA gene denaturing gradient gel electrophoresis fingerprinting and pyrosequencing. The communities also differed in their MCPA-mineralizing activities. The enrichments selected on low concentrations mineralized MCPA with shorter lag phases than those selected on high concentrations. Flow cytometry measurements revealed that mineralization led to cell growth. The presence of low-nucleic acid-content bacteria (LNA bacteria) was correlated with mineralization activity in cultures selected on low herbicide concentrations. This suggests that LNA bacteria may play a role in degradation of low herbicide concentrations in aquifers impacted by agriculture. This study shows that subpopulations of herbicide-degrading bacteria that are adapted to different pesticide concentrations can coexist in the same environment and that using a low herbicide concentration enables enrichment of apparently oligotrophic subpopulations.

Sorption, desorption, and degradation of (4-chloro-2-methylphenoxy)acetic acid in representative soils of the Danubian Lowland, Slovakia

Herbicide leaching through soil into groundwater greatly depends upon sorption-desorption and degradation phenomena. Batch adsorption, desorption and degradation experiments were performed with acidic herbicide MCPA and three soil types collected from their respective soil horizons. MCPA was found to be weakly sorbed by the soils with Freundlich coefficient values ranging from 0.37 to 1.03 mg(1-1/)(n) kg(-1) L(1/)(n). It was shown that MCPA sorption positively correlated with soil organic carbon content, humic and fulvic acid carbon contents, and negatively with soil pH. The importance of soil organic matter in MCPA sorption by soils was also confirmed by performing sorption experiments after soil organic matter removal. MCPA sorption in these treated soils decreased by 37-100% compared to the original soils. A relatively large part of the sorbed MCPA was released from soils into aqueous solution after four successive desorption steps, although some hysteresis occurred during desorption of MCPA from all soils. Both sorption and desorption were depth-dependent, the A soil horizons exhibited higher retention capacity of the herbicide than B or C soil horizons. Generally, MCPA sorption decreased in the presence of phosphate and low molecular weight organic acids. Degradation of MCPA was faster in the A soil horizons than the corresponding B or C soil horizons with half-life values ranging from 4.9 to 9.6 d in topsoils and from 11.6 to 23.4 d in subsoils.